1. Field of the Invention
The present invention relates to incendiary compositions. More particularly, the incendiary composition of the present invention contains a CTBN binder to improve ESD sensitivity of titanium/boron/polytetrafluoroethylene compositions. Most particularly, the CTBN binder is present in amounts of from about 10% or less combined with polytetrafluoroethylene in amounts of from about 20% or more.
2. Brief Description of the Related Art
Reducing the electrostatic discharge sensitivity (ESD) for dry metals is particularly important in the manufacture of incendiary devices. Highly reactive metals provide an excellent source for high burn temperatures, however, the more reactive the metal powders are, the more ESD sensitive they become. ESD sensitive metal powders are likely to ignite during handling or mixing, increasing hazards to personnel and manufacturing equipment. Combinations of titanium and boron potentially possess extremely high ESD sensitivity, with ignition of approximately 0.0084 joules possible. Other types of metallic mixtures that are less ESD sensitive, such as iron oxide and aluminum, i.e., Thermite, burn too quickly and with relatively low flame temperatures. Some combinations of magnesium, teflon and Viton A, e.g., MTV, have a high flame temperature, but they don""t have the slow burning rate.
In view of the foregoing, there is a need for improved incendiary compositions for having a low slag, low ESD sensitivity and high flame temperature. The present invention addresses this need.
The present invention includes a low slag, high temperature incendiary composition 15 comprising a reactive material of titanium, a second reactive material of boron, an oxidizer of polytetrafluoroethylene in an amount of from about 20 weight percent or greater of the composition and a CTBN binder in an amount of from about 10 weight percent or less, wherein the ratio of titanium to boron ranges from about 81/19 to about 69/31.
The present invention also includes a method of producing a low slag, high temperature incendiary composition comprising the steps of mixing a first combination of a reactive material of titanium with a second reactive material of boron and an oxidizer of polytetrafluoroethylene, wherein the polytetrafluoroethylene comprises an amount of from about 20 weight percent or greater of the composition and the ratio of titanium to boron ranges from about 81/19 to about 69/31 and adding a CTBN binder in an amount of from about 10 weight percent or less to the first combination.
Additionally, the present invention includes a high flame temperature product from the process comprising the steps of providing an incendiary composition of titanium, boron, polytetrafluoroethylene in an amount of from about 20 weight percent or greater of the composition, with the ratio of titanium to boron ranges from about 81/19 to about 69/31, and adding a CTBN binder in an amount of from about 10 weight percent or less, and igniting the composition.
Furthermore, the present invention includes a low slag, high temperature incendiary composition product from the process comprising the steps of mixing a first combination of a reactive material of titanium with a second reactive material of boron and an oxidizer of polytetrafluoroethylene, wherein the polytetrafluoroethylene comprises an amount of from about 20 weight percent or greater of the composition and the ratio of titanium to boron ranges from about 81/19 to about 69/31 and adding a CTBN binder in an amount of from about 10 weight percent or less to the first combination.
The present invention provides an incendiary composition having a low slag and high flame temperature that is safer to handle and mix because of a reduced sensitivity to ESD.
The present invention relates to incendiary compositions with improved electrostatic discharge (ESD) sensitivity. The incendiary compositions contain a carboxyl-terminated butadiene/acrylonitrile copolymer (CTBN) binder to improve ESD sensitivity of titanium, boron and polytetrafluoroethylene composition mixtures. The incendiary compositions are safe to handle, ignite readily, provide low slag and produce a very high flame temperature.
Safe ESD sensitivity for manufacture and handling of the present invention is in the range greater than 0.023 joules. The human body is capable of producing approximately 0.0084 joules. The high temperature incendiary composition of the present invention contains a reactive material of titanium, a second reactive material of boron, an oxidizer of polytetrafluoroethylene, which further includes a CTBN binder that increases the ESD resistance for the titanium/boron/polytetrafluoroethylene combination to a value of more than 0.023 joules.
Low slag for the present invention includes a slag percentage of less than 30% at a compaction of approximately 50% of the theoretical maximum density (TMD) of the composition. The slag is defined as the amount of solids that remain as a solid mass, at or near the location where the material is burned. A primary use for the present invention is to heat the air and surroundings to a high temperature. Therefore the hot particles produced from the burning need to transfer their heat to the air as quickly and efficiently as possible. The less solid slag produced, the more fine particles are ejected into the air and the more efficient is the transfer process.
Calculations show that mixture of the two reactive metals, titanium and boron, form an intermetallic compound together upon ignition. Solid titanium and boron react to form a liquid, i.e., molten, intermetallic compound, indicated by the formula:
Ti+2Bxe2x86x92TiB2
Other by-products occur, most significantly with the reaction of boron with polytetrafluoroethylene, and the reaction of the CTBN binder ingredients with titanium.
The titanium preferably comprises a particle size of from greater than 44 microns to about 150 microns, with ESD sensitivity increasing to unsafe levels below 44 microns and burn rates increasing beyond a slow burn rate above a particle size of from about 150 microns. Particle sizes of about 200 microns provide a burning rate of approximately 4.7 inches per minute or 321 grams per minute. Appropriate particle sizes for the titanium within the particle size range of from about 44 microns to about 150 microns may be used as determine by those skilled in the art for a given purpose in light of the disclosure herein. Boron particles may include any acceptable size, such as from about 0.5 microns to about 1 micron in size, as determined by one of ordinary skill in the art. The chemicals are commercially available in finely divided powders. Titanium powder metal is available from Atlantic Equipment Engineers of Bergenfield, N.J. under the catalog number TI-109, having a purity of 99.7%. Boron is available from Callery Chemical Company of Pittsburgh, Pa. under the tradename SB 95 having from about 95% to about 97% boron and from about 5% to about 3% magnesium oxide (MgO) or SB 90 having from about 90% to about 92% boron and from about 10% to about 8% magnesium oxide (MgO), with both products having an amorphous state with an average particles size of approximately 0.6 microns. Titanium amounts preferably include from about 41 weight percent to about 61 weight percent, and more preferably from about 51 weight percent to about 61 weight percent, with boron in amounts of from about 11 weight percent to about 24 weight percent, more preferably from about 14 weight percent to about 24 weight percent. For example, titanium may comprise approximately 60.75 weight percent and boron approximately 14.25 weight percent of the total composition.
The weight ratio amount of titanium to boron needed for a high flame temperatures range from about 81/19 to about 69/31. Preferably within this range, the titanium and boron are present in the composition in substantially stoichiometric proportions for forming the intermetallic compound. As the ratio of titanium to boron decreases, the combination metal becomes increasingly more difficult to ignite, with the proper ratio of titanium to boron for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein.
The incendiary composition includes an oxidizer of polytetrafluoroethylene, also known as Teflon(copyright), in an amount of from about 20 weight percent or greater of the composition. Preferred amounts of polytetrafluoroethylene range from about 20 weight percent to about 30 weight percent, with more preferred amounts of polytetrafluoroethylene ranging from about 20 weight percent to about 25 weight percent. The particles of the polytetrafluoroethylene may be any suitable size, such as from about 20 microns to about 450 microns, with little affect on the burning rate or slag percentage. As the amount of polytetrafluoroethylene increases, the reaction energy of the titanium/boron ignition decreases, with the proper amount of polytetrafluoroethylene for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein. Polytetrafluoroethylene is available from E.I. duPont de Nemours and Company of Wilmington, Del. under the tradename Teflon(copyright) 7C.
The CTBN binder is included within the incendiary composition in an amount of from about 10 weight percent or less. Preferred amounts of CTBN binder range from about 4 weight percent to about 6 weight percent, with more preferred amounts of carboxyl-terminated acrylonitrile being approximately 5 weight percent. CTBN binder is a liquid at ordinary temperatures but when heated will cure to form a rubber-like material. As the amount of CTBN binder increases, the flame temperature decreases and slag increases, with the proper amount of CTBN binder for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein. CTBN is available from B.F. Goodrich Company in Breckville, Ohio under the Hycar(copyright) 1300 series of polymers. The CTBN may be accompanied by additive components determinable by one skilled in the art including plasticizers such as dioctyl adipate (DOA) available from Union Camp Corporation in Wayne, N.J.; wetting agents such as lecithin (soy phospholipids, phosphatides) available from American Lecithin Company in Danbury, Conn.; crosslinkers such as Araldite(copyright) MY 0510 (4-glycidyloxy-N,N-Diglycidylaniline) available from Ciba Specialty Chemicals Corporation in Brewster, N.Y.; and/or curing catalysts such as Fomrez(copyright) C-2 (stannous octoate) available from Witco Chemicals, Organic Division in Huston, Tex. For examples, the 10% CTBN binder may be composed of 4.70% CTBN, 2.60% DOA, 2.00% lecithin, 0.62% Araldite MY 0510, and 0.08% Fomrez C-2, with the percentages of the additives in the binder are decreased proportionately as the CTBN binder decreases. The percentages of the additives in the binder can also vary as necessary to achieve certain characteristics as determinable by one skilled in the art of formulating.
The incendiary composition may be manufactured in a safe manner by using the binder to decrease the electrostatic discharge hazard during handling and mixing. The preferred method for preparing the invention includes adding the non-binder components, i.e., titanium, boron and polytetrafluoroethylene, into a bowl before mixing, but other procedures were successfully used in the small scale development mixes. After the component powders are added, the electrostatic field (E-field) is measured. A commercially available electrostatic fieldmeter is used and measurement is determined according to the manufacturer""s directions. E-field measurements of 3 kilovolts per inch or less permit the method to proceed, with the addition of the CTBN binder. Once the CTBN binder has been added, the components are mixed for a total of approximately two and one-halfhours. Every half hour, during the first two and one hours, the mix is stopped and the blades and sides of the bowl are scrapped with a conductive spatula.
A high flame temperature product results with the ignition of the incendiary composition of the 81/19 to 69/31 ratio of titanium and boron, 20 weight percent or more polytetrafluoroethylene and 10 weight percent or less CTBN binder. Temperatures of the incendiary composition igniting may range from about 3500xc2x0 F. or higher, with temperatures from about 4000xc2x0 F. to about 5000xc2x0 F. preferred, such as approximately 4600xc2x0 F. As the incendiary composition comprises lesser amounts of CTBN binder, such as 5 weight percent or less, the flame temperature increases. As the incendiary composition comprises less polytetrafluoroethylene, such as from about 20 weight percent to about 25 weight percent, the reaction energy increases.